Question

I would like to create an INTERSECTion of the following two queries using MySQL:

1) SELECT atn_nid, atn_select_flag, atn_image_name
FROM city, attraction WHERE cty_nid = atn_cty_nid AND cty_nid = 5;

2) SELECT atn_nid, s2a_image_select_flag, atn_image_name 
FROM segment, seg2atn, attraction WHERE seg_nid = s2a_seg_nid AND
s2a_atn_nid = atn_nid and seg_nid = 68 AND
s2a_image_select_flag = true;  

Note: The atn_select_flag in Query 1 and the s2a_image_select_flag are both Boolean

Since MYSQL for some reason does not support INTERSECT, I am at a loss as to the syntax to use to accomplish this. Any help would be gratefully appreciated.

Answer 1

If I assume correctly that:

• fields named atn_..., cty_..., seg_..., and s2a_... belong to attraction, city, segment, and seg2atn, respectively.
• fields named ..._nid are primary keys.
• atn_cty_nid, s2a_seg_nid, etc., are foreign keys.

then your first query is equivalent to this:

SELECT atn_nid, atn_select_flag, atn_image_name
  FROM attraction
 WHERE aty_cty_nid = 5
;

and your second query is equivalent to this:

SELECT atn_nid, TRUE, atn_image_name
  FROM attraction
 WHERE atn_id IN
        ( SELECT s2a_atn_nid
            FROM seg2atn
           WHERE s2a_seg_nid = 68
             AND s2a_image_select_flag = TRUE
        )
;

so their intersection is this:

SELECT atn_nid, TRUE AS atn_select_flag, atn_image_name
  FROM attraction
 WHERE atn_cty_nid = 5
   AND atn_nid IN
        ( SELECT s2a_atn_nid
            FROM seg2atn
           WHERE s2a_seg_nid = 68
             AND s2a_image_select_flag = TRUE
        )
;

and (edited to add) their union is this:

SELECT atn_nid, atn_select_flag, atn_image_name
  FROM attraction
 WHERE aty_cty_nid = 5
UNION
SELECT atn_nid, TRUE, atn_image_name
  FROM attraction
 WHERE atn_id IN
        ( SELECT s2a_atn_nid
            FROM seg2atn
           WHERE s2a_seg_nid = 68
             AND s2a_image_select_flag = TRUE
        )
;